Our long term goal is to understand the molecular basis of pattern formation in the lower eukaryote Dictyostelium. We are interested in particular how cyclic AMP acts to regulate gene expression in this organism and higher eukaryotes as well. We consider our work to be relevant to pattern formation during early embryogenesis and later, for example, during limb formation. Our principal method of analysis is to isolate mutants that are defective in a developmental process and to analyze their defects by any genetic or biochemical method. Our specific aims here are (1) to prepare monoclonal antibodies that recognize prespore and prestalk cell surface antigens, (2) to isolate mutants that do not differentiate as stalk cells in the presence of cyclic AMP, (3) to analyze cyclic AMP-dependent regulation of translation in vitro, and (4) to improve a method for inactivation of differentiation genes by mutagenic insertion.